An embodiment of the invention relates to printed circuit board layout techniques.
A printed wiring board, also referred to as a printed circuit board, is a structure that communicatively interconnects a number packaged integrated circuits (i.e., ICs), as part of an electronic system. For example, every notebook and desktop personal computer has a motherboard on which processor, system chipset, and main memory IC packages are installed. Each package is electrically connected to a separate group of conductive pads that are formed on a surface of the board. These pads may be referred as having a xe2x80x98footprintxe2x80x99 of that package. The pad to package connection may be made by, for instance, direct soldering the package to the pads, or mounting the package on a socket that itself is soldered to the pads.
The board has conductive signal lines formed in one or more signal routing layers. A signal line is typically routed between, and electrically connects, a pad for one package and one or more corresponding pads for another package. The process of determining or creating a route for a signal line to go from a pad within a footprint to a location outside of the footprint, without being too close or touching other pads or signal lines, is called xe2x80x98breaking out the signalxe2x80x99.
To support complex logic functions, an IC package uses a large number of signals and hence requires a correspondingly large number of pads in its footprint. If the signals that are to be broken out of a footprint are too numerous to fit on a single routing layer of a board, then additional routing layers must be provided in the board to break out all of the remaining signals. Each additional layer, however, may substantially increase the cost of manufacturing the board.